The present invention relates generally to the field of solid state safety relays, and more particularly to a solid state safety relay with two (redundant) drive circuits for driving MOSFET transistors that function as switches.
Mechanical relays are used in various applications. For example, mechanical relays are used to control the flow of current across wires in a circuit. However, conventional mechanical relays have various mechanical limitations. For example, in most cases, mechanical relays cannot operate reliably in both xe2x80x9cwetxe2x80x9d and xe2x80x9cdryxe2x80x9d circuit conditions. A wet circuit is defined as a circuit that, by virtue of the current/voltage applied across the relay contacts, has the ability to clean its own contacts. A dry circuit is defined as a circuit that applies very low power across the relay contacts, and, as a result, is unable to clean its own contacts.
Another limitation of conventional mechanical relays is that they are subject to many forms of environmental contamination and physical degradation.
The above drawbacks are not acceptable if the mechanical relay is used in particular critical applications such as safety devices. The above limitations of mechanical relays may cause a safety device to fail during operation.
Thus there is a need for a solid state based relay that would overcome the many drawbacks and limitations of conventional mechanical relays.
The present invention broadly provides a solid state safety relay which includes redundant circuitry for blocking the flow of current in the discharge direction. The redundant circuitry enables an energy source (e.g., a battery) to be disconnected from the relay circuit regardless of any single point of failure that may occur in the relay circuit. As a result, the safety relay is useful in critical applications such as safety devices.
The present invention broadly provides in one embodiment a solid state safety relay comprising: a first driver circuit; a second driver circuit; a charge disconnect transistor coupled to the first driver circuit and configured to control the flow of current along a current path; a first discharge disconnect transistor coupled to the first driver circuit and configured to control the flow of current along the current path; and a second discharge disconnect transistor coupled to the second driver circuit and configured to control the flow of current along the current path. The charge disconnect transistor controls the flow of current in the charge direction, while each of the discharge disconnect transistors controls the flow of current in the discharge direction.
In another embodiment, the solid state safety relay further comprises: a third driver circuit coupled to the first and second driver circuit; a second charge disconnect transistor coupled to the third driver circuit and configured to control the flow of current along a second current path; and a third discharge disconnect transistor coupled to the third driver circuit and configured to control the flow of current along the second current path.
The present invention also provides in another embodiment a solid state safety relay comprising: a first driver circuit; a second driver circuit; a first discharge disconnect transistor coupled to the first driver circuit and configured to control the flow of current along the current path; and a second discharge disconnect transistor coupled to the second driver circuit and configured to control the flow of current along the current path.
The present invention also provides in another embodiment a method of isolating a battery source from a circuit current path, comprising: turning off a first discharge disconnect transistor coupled to the circuit current path; and turning off a second discharge disconnect transistor coupled to the circuit current path to permit isolation of the battery source from the circuit current path if either one of the first discharge disconnect transistor or the second discharge disconnect transistor fails.